1. Field of the Invention
The present invention relates to a printed circuit board on a backplane and a method of data transmission on the backplane.
2. Description of the Related Art
Recently, a processing speed of a data processor or a transmitter has been improved. A data transmission speed inside a device which is used to be several hundred megabits per second (Mbps) has increased to more than 1 Giga-bps. Due to the increase in the data transmission speed inside the device, a reflected wave that is generated along with data transmission causes a distortion of a signal waveform, resulting in a data transmission error.
If the data transmission speed is low, even if a reflected wave is generated in a transmission line in the device, the generated reflected wave falls within a 1-bit timeslot and does not affect timeslots of other bits. However, if the data transmission speed is increased and the 1-bit timeslot is reduced, the reflected wave affects the other timeslots. Due to this, a receiver of data is not able to correctly determine whether a bit is on or off.
Especially, in a data processor or a transmitter such as a blade server which includes a plurality of printed circuit boards connected through a backplane, the problem of reflected waves is significant. This is because a device having such a structure includes a connector for mounting a printed circuit board on a backplane therein. The connector is likely to generate a reflected wave due to impedance mismatch.
There are known technologies as disclosed in, for example, Japanese Patent Application Laid-open No. S59-081928 to reduce the influence of reflected waves by generating cancellation waves to cancel the reflected waves.
Depending on a configuration of a transmission line, reflected waves sometimes repeatedly travel back and forth in a predetermined section of the transmission line while attenuating and exerting influence on a plurality of bits. Moreover, if waveforms of the reflected waves and data transmission waveforms overlap many times, the waveforms of the reflected waves become large due to resonance. This may cause a significant data transmission error.
However, such characteristics of the reflected waves are not sufficiently taken into consideration in the conventional technologies for reducing the influence of the reflected waves. Consequently, the influence of the reflected waves in data transmission cannot be sufficiently eliminated.